3-azabicyclo(3.1.0)hexane-2-carboxylic acid has been found to be an effective plant male gametocide: U.S. Pat. No. 4,047,930 (the compound is designated therein as 2-carboxy-3,4-methanopyrrolidine). The compound exists in the forms of two geometric (i.e., cis, trans) isomers. Each of these isomeric forms exists in the forms of optical isomers. The racemic mixtures of both of the geometric isomer forms are active as plant male gametocides. The naturally occurring L,cis isomer is active as a plant male gametocide; the relative activities of each of the other optical isomer forms have not been determined. The L,cis isomer occurs naturally in the seeds of the American horse chestnut.